Method of discharge coating and an apparatus therefor

Abstract

A discharge coating apparatus comprises an assembly for applying a vibrational motion in the longitudinal direction of an electrode while applying a voltage pulse in synchronization with the vibration to cause electrical discharge between the surface of a workpiece and the electrode and the formation of a coating layer on the workpiece of the material of the electrode due to the heat produced by the electrical discharge. An additional motion is applied to the electrode to cause the electrode to undergo reciprocal travel towards and away from the suirface of the workpiece at an angle relative thereto. The additional motion can be a rotational motion. The electrode can be formed with a concave portion at its tip or with an axial bore so that only an annulus of the electrode contacts the workpiece. The additional motion can be a skipping movement by utilizing a skipping mechanism consisting of an elastic memebr.

What is claimed is: 
     
       1. In a method of forming a coating layer on a member to be coated, comprising the steps of placing an electrode of a coating material in opposing facing relation with the surface of the member to be coated with the coating material; applying a mechanical vibration to said electrode to cause the electrode to successively come into contact with and be removed from the surface of said member while supplying electrical current to the electrode and member thereby forming a coating layer on the surface of the member, the improvement comprising the steps of: applying to the coating material electrode an additional motion to cause the tip of the electrode to perform a sliding motion parallel to the surface of said member in addition to said mechanical vibration while supplying said current to the electrode and member, said electrode having a longitudinal central axis and said vibration being applied to said electrode in the direction of its longitudinal central axis, said additional motion being a rotational motion about an axis of rotation at a rotational speed of 500 to 6000 rpm, said electrode being devoid of material along said axis of rotation. 
     
     
       2. In a method of forming a coating layer on a member to be coated, comprising the steps of placing an electrode of a coating material in opposing facing relation with the surface of the member to be coated with the coating material; applying a mechanical vibration to said electrode to cause the electrode to successively come into contact with and be removed from the surface of said member while supplying electrical current to the electrode and member thereby forming a coating layer on the surface of the member, the improvement comprising the steps of: applying to the coating material electrode an additional motion to cuase the tip of the electrode to perform a sliding motion parallel to the surface of said member in addition to said mechanical vibration while supplying said current to the electrode and member, said electrode having a longitudinal central axis and said vibration being applied to said electrode in the direction of its longitudinal central axis, said additional motion being a rotational motion about an axis of rotation so that said electrode slides on the surface of said member during a period of time when the coating material electrode is in contact with the surface of said member for at least 10 μm, said electrode being devoid of material along said axis of rotation. 
     
     
       3. A surface treating method as claimed in claim 1 or 2, wherein the axis of rotation of said electrode is coincident with its longitudinal central axis and said electrode is formed as a tubular element. 
     
     
       4. A surface treating method as claimed in claim 1 or 2, wherein the axis of rotation of said electrode is coincident with its longitudinal central axis and the electrode is formed by a hollow central portion. 
     
     
       5. A surface treating method as claimed in claim 1 or 2, wherein the axis of rotation of said electrode is coincident with its longitudinal central axis and said electrode is formed by a plurality of thin wires secured together to form a hollow tube. 
     
     
       6. A surface treating method as claimed in claim 1 or 2, wherein, said additional motion further includes a vibrational motion which is perpendicular to said longitudinal central axis. 
     
     
       7. A surface treating method as claimed in claim 1 or 2 comprising elastically pressing said electrode against the surface of said member to produce a skipping motion in addition to said sliding motion. 
     
     
       8. A surface treating method as claimed in claim 1 or 2, wherein said electrode is caused to undergo a composite motion consisting of said vibration and said additional motion to apply the coating layer on said member in the form of overlapping fish scales. 
     
     
       9. A discharge coating apparatus comprising: a base including upstanding columns;   a table movably mounted on said base and including means for supporting a member onto which a coating layer is to be applied;   first travelling means for moving said table;   a cross beam slidably supported by said columns;   second travelling means for moving said cross beam along said columns;   at least one machining head comprising a carriage supported by said cross beam for movement in a direction perpendicular to the direction of movement of said table; electrode attaching means on said carriage for supporting an electrode composed of the material to form the coating layer on said member, said electrode having a central longitudinal axis; electrode vibrating means for vibrating said electrode attaching means along the longitudinal axis of the electrode; means for rotating said electrode attaching means about an axis of rotation to apply an additional motion to said electrode attaching means in a direction perpendicular to the direction of vibration thereof without obstructing the motion of said electrode attaching means; said electrode being devoid of material along said axis of rotation; and current pulse to said electrode to effect discharge coating of said member by the material of said electrode while also supplying electrical power to said first and second travelling means, said electrode vibrating means and said means for applying additional motion to said electrode attaching means without obstructing the motion of said electrode attaching means; and   controller means for controlling the motions of said first and second travelling means and said machining head such that said electrode undergoes a composite movement comprising said vibration along the longitudinal axis of the electrode together with said additional motion whereas said table is moved to cause a coating layer of the material of the electrode to be applied to said member.   
     
     
       10. A discharge coating apparatus as claimed in claim 9, wherein said electrode vibrating means comprises an electromagnet and a leaf spring which rotatably holds said electrode attaching means and is attracted and vibrated by said electromagnet. 
     
     
       11. A discharge coating apparatus as claimed in claim 10, wherein said means for applying the additional motion comprises a motor connected to rotate said electrode attaching means, said axis of rotation being offset from said longitudinal axis of said electrode. 
     
     
       12. A discharge coating apparatus as claimed in claim 9, wherein said current supplying means comprises a DC power supply connected to said electrode and the member to be coated, a switching element in said DC power supply, and means for controlling said switching element. 
     
     
       13. A discharge coating apparatus as claimed in claim 9, wherein said current supplying means comprises a DC power supply, inductive coupling means having a primary side connected to said DC power supply and a secondary side connected to said electrode and the member to be coated and a switching element connecting the DC power supply to said primary side; and means for controlling said switching element. 
     
     
       14. A discharge coating apparatus comprising: a base including upstanding columns;   a table movably mounted on said base and including means for supporting a member onto which a coating layer is to be applied;   first travelling means for moving said table;   a cross beam slidably supported by said columns;   a second travelling means for moving said cross beam along said columns;   at least one machining head comprising a carriage supported by said cross beam for movement in a direction perpendicular to the direction of movement of said table; a motor attached to said carriage and including an output shaft having an axis of rotation; electrode attaching means connecting an electrode thereof; elastic means connecting said electrode attaching means to the output shaft of said motor such that the electrode attaching means is driven in rotation around said axis of rotation of said output shaft; electrode vibrating means for vibrating said electrode attaching means, said electrode being devoid of material along said axis of rotation; and current supplying means for supplying a current pulse to said electrode to effect discharge coating of said member by the material of said electrode while also supplying electrical power to said motor and said electrode vibrating means without obstructing the motion of said electrode attaching means; and   controller means for controlling the operations of said first and second travelling means and said machining head such that said electrode undergoes a composite movement comprising said vibration along the longitudinal axis of the electrode together with said rotational motion whereas said table is moved to cause a coating layer of the material of the electrode to be applied to said member.   
     
     
       15. A discharge coating apparatus as claimed in claim 14, wherein said electrode vibrating means comprises one electromagnet and a leaf spring which rotatably holds said electrode attaching means and is attracted and vibrated by said electromagnet. 
     
     
       16. A discharge coating apparatus as claimed in claim 14, wherein said elastic means comprises a helical, torsional, coil spring which causes said electrode to undergo a skipping when the electrode comes into contact with the surface of the member to be coated while preventing transmission of vibration of the electrode to the motor. 
     
     
       17. A discharge coating apparatus as claimed in claim 14, wherein said elastic means comprises a volute spring which causes said electrode to undergo a skipping motion when the electrode comes into contact with the surface of the member to be coated while preventing transmission of vibration of the electrode. 
     
     
       18. A discharge coating apparatus as claimed in claim 14, wherein said current supplying means comprises a DC power supply connected to said electrode and the member to be coated, a switching element in said DC power supply, and means for controlling said switching element. 
     
     
       19. A discharge coating apparatus as claimed in claim 14, wherein said current supply means comprises a DC power supply, inductive coupling means having a primary side connected to said DC power supply and a secondary side connected to said electrode and the member to be coated and a switching element connecting the DC power supply to said primary side, and means for controlling said switching element. 
     
     
       20. A discharge coating apparatus comprising: a bed;   a cross table movably mounted on said bed and including means for mounting a member onto which a coating layer is to be applied;   travelling means for moving said cross table;   a column upstanding on said bed;   an arm supported by said column;   a head comprising a housing supported by said arm for movement in a direction perpendicular to the direction of movement of said cross table; a motor attached to said housing, said motor including an output shaft having an axis of rotation; elastic means; a vibrating stem having a longitudinal axis, said stem being attached by said elastic means to the output shaft of said motor for rotation therewith around said axis of rotation; electrode attaching means on said stem for supporting an electrode composed of the material to form the coating layer on said member, said electrode being supported in said electrode attaching means and being devoid of material along said axis of rotation of said output shaft; vibrating means for applying vibration to said vibrating stem along its longitudinal axis without obstructing rotation of the vibrating stem; and current supplying means for supplying a current pulse to said electrode while also supplying electrical power to said motor and said vibrating means without obstructing the motion of said vibrating stem; and   controller means for controlling the operations of said travelling means and said head.   
     
     
       21. A discharge coating apparatus as claimed in claim 20, wherein said vibrating means comprises at least one vibrating coil, and an iron core fixedly attached to said vibrating stem for being attracted to said vibration generating coil. 
     
     
       22. A discharge coating apparatus as claimed in claim 20, wherein said elastic means comprises a helical, torsion, coil spring which causes said electrode to undergo a skipping motion when said electrode comes into contact with the surface of the member to be coated while preventing transmission of vibration of the electrode to said motor. 
     
     
       23. A discharge coating apparatus as claimed in claim 20, wherein said elastic means comprises a volute spring which causes said electrode to undergo a skipping motion when said electrode comes into contact with the surface of the member to be coated while prventing transmission of vibration of the electrode to said motor. 
     
     
       24. A discharge coating apparatus as claimed in claim 20, wherein said current supplying means comprises a DC power supply connected to said electrode and the member to be coated, a switching element in said DC power supply, and means for controlling said switching element. 
     
     
       25. A discharge coating apparatus as claimed in claim 20, wherein said current supplying means comprises a DC power supply, inductive coupling means having a primary side connected to said DC power supply and a secondary side connected to said electrode and the member to be coated and a switching element connecting the DC power supply to said primary side; and means for controlling said switching element. 
     
     
       26. Apparatus for forming a coating layer on the surface of a member to be coated, said apparatus comprising means for supporting a member onto which a coating layer is to be applied, means for supporting, in confronting relation with said member, an electrode composed of the material of the coating layer to be applied to said member, means for providing relative movement between said electrode and said member which movement is composed of a reciprocal movement of the electrode towards and away from said member and an additional movement at an angle to said reciprocal movement such that the electrode periodically contacts and moves away from the surface of the member at an acute angle relative thereto, means for supplying electrical energy to said electrode during at least a portion of the periods of contact between the electrode and the surface member to cause melt adherence of the material of the electrode on the surface of the member, and means for providing further relative movement between the electrode and said member in a direction along the surface of the member to be coated so as to extend the melt adherence of the material of the electrode along a given region of the surface of the member, said reciprocal movement being perpendicular to the surface of the member to be coated and said additional movement being perpendicular to said reciprocal movement; said further relative movement being parallel to the surface of said member, said additional movement being a rotational movement of a rotational speed of 500 to 6000 rpm about an axis parallel to the direction of reciprocal movement between the electrode and the member, said electrode having a longitudinal axis and being devoid of material along the axis of rotational movement. 
     
     
       27. Apparatus for forming a coating layer on the surface of a member to be coated, said apparatus comprising means for supporting a member onto which a coating layer is to be applied, means for supporting, in confronting relation with said member, an electrode composed of the material of the coating layer to be applied to said member, means for providing relative movement between said electrode and said member which movement is composed of a reciprocal movement of the electrode towards and away from said member and an additional movement at an angle to said reciprocal movement such that the electrode periodically contacts and moves away from the surface of the member at an acute angle relative thereto, means for supplying electrical energy to said electrode during at least a portion of the periods of contact between the electrode and the surface member to cause melt adherence of the material of the electrode on the surface of the member, and means for providing further relative movement between the electrode and said member in a direction along the surface of the member to be coated so as to extend the melt adherence of the material of the electrode along a given region of the surface of the member, said reciprocal movement being perpendicular to the surface of the member to be coated and said additional movement being perpendicular to said reciprocal movement; said further relative movement being parallel to the surface of said member, said additional movement being a rotational movement of a rotational speed of 500 to 6000 rpm about an axis parallel to the direction of reciprocal movement between the electrode and the member wherein said electrode slides on the surface of said member due to said additional motion during a period of time when the electrode is in contact with the surface of said member for at least 10 μm, said electrode having a longitudinal axis and being devoid of material along the axis of rotational movement. 
     
     
       28. Apparatus as claimed in claim 26 or 27, wherein said rotational travel of said additional movement is angularly reciprocal. 
     
     
       29. Apparatus as claimed in claim 26 or 27 comprising elastic means acting on said electrode for urging the electrode towards said member.